In the past two decades, the market for wireless communication systems has shown unprecedented growth. In addition to the widespread proliferation of mobile phone services, wireless local area networks (WLANs) operating according to wireless standards such as IEEE 802.11a, IEEE 802.11b and IEEE 802.11 g are becoming more common. As the popularity of wireless systems increases, so does the demand for improved performance in the wireless transceivers supporting such systems.
One of the components in a wireless transceiver that can affect performance is the power amplifier. For example, linear power amplifiers are often used in mobile transceivers to amplify radio frequency (RF) signals to be transmitted from the transceiver. Linear amplification is typically required in such transceivers to support the signal processing methods used to encode the RF transmissions (for example, Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or Enhanced Data GSM Environment (EDGE) processing). Further, because of the mobile nature of many wireless devices, the power amplification required for proper transmission is not necessarily constant. Consider, for example, a typical CDMA handset used in a cellular telephone network. Typical CDMA handsets are desirably capable of producing output powers of up to +28 dBm. The average output power that is necessary for such handsets, however, is far less than this maximum, and is generally closer to 0 dBm. The power required for proper transmission is typically dependent on the distance of the handset to the corresponding base station, and thus varies as the handset is transported from location to location. Further, because the typical handset draws its power from the handset battery, operating the linear power amplifier with optimal efficiency at the various required power levels would extend battery life, and thus the talk time of the handset. Accordingly, there exists a need for improved amplifiers that can operate with enhanced efficiency in multiple power modes, thereby providing the necessary peak power in one mode and efficient, low-power operation in another.